Aneurysm is a permanent limitation expansion of the blood vessel and it is called an aneurysm when the vessel diameter is increased by more than 50% of its normal size, If an aneurysm is in the abdominal aorta, an abdominal aortic aneurysm is formed. Iliac aneurysm is usually defined as the case that the local extension of the iliac artery diameter exceeds 1.5 cm. The iliac aneurysm is divided into isolated iliac aneurysm (see FIG. 1), independent iliac aneurysm (see FIG. 2), and iliac aneurysm accompanied by abdominal aortic aneurism (see FIG. 3). In 75% of the cases, iliac aneurysm is associated with abdominal artery. There are about 7.5% of the cases being isolated iliac aneurysm. The remaining aneurysm is the independent iliac aneurysm. In the United States, about 15,000 people die of abdominal aortic aneurysm (abdominal aortic aneurysm, AAA) rupture each year. It was believed in early reports that the iliac aneurysm having a diameter of more than 3 cm was fatal and it is recommended to be treated by surgery. Although this disease is thought to involve only 2% of the general population. it tends to occur in the elderly, and with the arrival of China's aging population, its incidence is rising.
As shown in FIG. 1 to FIG. 3, the abdominal iliac artery 1 includes the renal artery 11 on the abdominal aorta, the abdominal aorta 12, the right arteria iliaca communis 13, the right internal iliac artery 14, the right external iliac artery 15, the left arteria iliaca communis 16, the left internal iliac artery 17 and the left external iliac artery 18. The protein degradation of connective tissues in arterial walls, inflammation and immune responses, as well as other factors, result in the loss of elastin in the middle and outer membranes, which causes the extension of tumors. Single iliac aneurysm, being not accompanied by abdominal aortic aneurysm, is known as an isolated iliac aneurysm, such as the right iliac aneurysm 19 as shown in FIG. 1. Several iliac aneurysms, being not accompanied by abdominal aortic aneurysm, are known as independent iliac aneurysm, such as the right iliac aneurysm 19 and the left iliac aneurysm 20 as shown in FIG. 2. Aneurysms existing in abdominal aorta and iliac artery are called iliac aneurysms accompanied by abdominal aneurysm, such as the right iliac aneurysm 19, the left iliac aneurysm 20 and abdominal aortic aneursm 21 as shown in FIG. 3.
Either open surgery or endovascular surgery can be used to repair the iliac aneurysms. Open repair can be carried out on all iliac aneurysms under anatomical conditions to replace arterial segments having pathological changes with artificial blood vessels, with good long-term results; however, the complications and mortality of iliac aneurysm open repair are equivalent to those of a major vascular surgery.
In the minimally invasive interventional treatment techniques which make use of endovascular exclusion principle, a covered stem is usually adopted to cover the aneurysm. At present, the commercially available covered stem is mainly composed of wire and PET (polyethylene terephthalate resin) membrane or ePTFE (polytetrafluoroethylene) membrane covered thereon, and the metal stent is made into a cylindrical or bifurcated metal frame. The compressed covered stent is delivered to the location of pathological changes and accurately released by a delivery system, and with the help of a developing system to cover the aneurysm, the stent isolates pathological changes and forms a new blood flow channel so that the aneurysm and arterial pressure are isolated, and the blood remaining in the lumen of the aneurysm gradually forms thrombosis and vascular tissue by muscularization. The expanded aneurysm wall contracts due to the negative pressure, thereby eliminating the hidden risks of tumor rupture and bleeding so as to achieve the purpose of healing.
In comparison, at present, endovascular repair is adopted to treat iliac aneurysms, which can only block the bilateral internal iliac arteries or unilateral internal iliac artery, which may cause complications such as impotence, gluteus claudication and pelvic ischemic. Many clinical research data show that retaining at least one side of the internal iliac artery can significantly reduce the incidence of above-mentioned complications. At present, it has been reported in the literature that the internal iliac bifurcated stent in the treatment of iliac aneurysms can open the bilateral internal iliac arteries and significantly reduce or avoid complications caused by the internal iliac artery blocking, which has distinct advantages.
The proximal end and distal end of the stent can be defined by the blood flow, which flows from the proximal end to the distal end of the stent.
Currently, the covered stent used for interventional treatment in the lumen of the iliac communis aneurysm affecting the internal iliac artery mainly consists of two types, respectively a straight-tube type covered stent and a bifurcated stent graft, wherein the straight-tube type graft stent further includes two types, including one with a horn mouth at the distal end and the other one without a horn mouth at the distal end. The straight-tube type stent has a proximal end and a distal end. A bifurcated stent means that the stent has a proximal end of the body and two distal ends of the branch.
When the straight-tube type covered stent without a horn mouth at the distal end is adopted, the distal end of the stent must be released in the external iliac artery in order to ensure that the distal end of the stem has a reliable anchoring and that no endo-leak will occur. Thus, the covered stent will block the internal iliac artery, which will result in pelvic ischemia, thereby causing the occurrence of complications such as gluteus claudication, colon ischemia, spinal cord ischemia, perineum necrosis and sexual dysfunction,
When the straight-tube type covered stent with a horn mouth at the distal end is adopted, the distal end of the stent may be released approximate to the opening of the internal iliac artery and the stent with a horn mouth at the distal end is attached to the arteria iliaca communis wall. Thus, circulation of the internal iliac artery can be ensured; however, the stem does not completely isolate the arteria iliaca communis, which still carries the risk of rupture.
The bifurcated stem graft is composed of a body, a main branch and a side branch part. The body and the side branch are released in the arteria iliaca communis, with the distal end of the side branch being approximate to the internal iliac artery and the distal end of the main branch is released within the external iliac artery involved by no aneurysm. After the bifurcated stent graft has been completely released, an outer periphery covered stem is released into the internal iliac artery via the side branch and connected to the side branch. This ensures the circulation of the internal iliac artery and the complete isolation of the arteria iliaca communis. In summary, the bifurcated stent graft is a preferred option for the treatment of the arteria iliaca communis involving internal iliac artery. A common bifurcated stent graft comprises a body and a side branch, and an independent waveform ring is used to extend across the connection part of the body and the side branch of the stem, and surround a circle. However, because of irregular shape at the boundary between the body and the side branch, the independent waveform ring is hard to set, and the axial origination site of the side branch is not fully attached with the waveform ring, so that the side branch has insufficient radial support force at this site, resulting problems such as the covering film being likely to retract due to insufficient support force at this site, and difficulties for the guidewire to enter the side branch through the body.